Not applicable.
Not applicable.
Known in the present state of the art is a method for in-tube flaw detection (RU2018817xe2x80x94Aug. 30, 1994; RU2042946xe2x80x94Aug. 27, 1995; RU2108569xe2x80x94Apr. 10, 1998; U.S. Pat. No. 4,162,635xe2x80x94Jul. 31, 1979) by passing inside the pipeline the so-called xe2x80x9cpigxe2x80x9d or an inspection probe which carries reference transducers responsive to diagnostic parameters of pipelines, means for data measuring and processing, and for storing the measured data, by making periodical reference to said reference transducers which emit probing ultrasonic pulses and receiving respective reflected ultrasonic pulses.
Known in the art is another method for in-tube flaw detection (WO 96/13720xe2x80x94May 9, 1996 (relevant patent documents: U.S. Pat. No. 5,587,534, CA2179902, EP0741866, AU4234596, JP3058352);
EP0304053xe2x80x94Mar. 15, 1995 (relevant patent documents: U.S. Pat. No. 4,964,059, CA1292306, NO304398, JP1050903);
EP0271670xe2x80x94Dec. 13, 1994 (relevant patent documents: U.S. Pat. No. 4,909,091, CA1303722, DE3638936, NO302322, JP63221240);
EP0616692xe2x80x94Sep. 28, 1994 (relevant patent documents: WO93/12420, U.S. Pat. No. 5,635,645, CA2125565, DE4141123, JP2695702);
EP0561867xe2x80x94Oct. 26, 1994 (relevant patent documents: WO92/10746, U.S. Pat. No. 5,497,661, CA2098480, DE4040190)) based on a thickness metering technique. The method consists in passing the inspection pig provided with ultrasonic transducers, and means for measuring, processing, and storing the measured data, by periodically referring to said ultrasonic transducers that emit ultrasonic probing pulses, and by receiving respective reflected ultrasonic pulses, and by measuring the transit time of said pulses.
It is the repetition period of the ultrasonic probing pulse and the travel speed of the inspection pig (flaw detector) inside the pipeline that are responsible for longitudinal resolving power of the flaw detector. With a predetermined scanning period (i.e., the repetition period of probing pulses) the scanning increment depends on the travel speed of the inspection pig, i.e., the higher the pig travel speed the larger the scanning increment, and vice versa. The inspection pig travel speed in an oil pipeline or oil-product pipeline may amount to 2 m/s (an unsteady-state value up to 6 m/s), that in a gas pipeline, up to 10 m/s (provided that acoustic communication is established between the ultrasonic transducers and the pipeline wall using, e.g., a liquid plug). When the inspection pig is being passed through the pipeline, its travel speed changes, and in order that longitudinal resolving power be not in excess of a maximum permissible one, the repetition period of probing pulses is selected proceeding from a maximum travel speed of the inspection pig which is practicable when inspecting a particular pipeline.
As a result of changes in the inspection pig travel speed during its passing through the pipeline, an excessive scanning occurs on the travel portions where the inspection pig travel speed is decreased (with the preset rate of referring to the reference transducers), said excessive scanning resulting in an increased amount of measured data per unit length of pipeline and, accordingly, in unreasonable use of the data storage element.
Furthermore, dynamic scanning is performed, according to the method discussed above, whereby the scanning conditions depend on the inspection pig travel speed, as well as on the nature of changes in the travel speed of the flaw detector.
Known in the present state of the art is one more method for in-tube ultrasonic flaw detection of thin-walled pipes of heat-exchangers (U.S. Pat. No. 5,062,300xe2x80x94Nov. 5, 1991 (relevant patent documents: CA1301299, EP0318387, DE3864497, FR2623626, JP2002923)) by passing inside a pipeline a tube-mounted inspection pig having ultrasonic transducers and measurement means, said method consisting in periodically referring to ultrasonic transducers emitting ultrasonic probing pulses and receiving the respective reflected ultrasonic pulses, and processing the measured data. This method is characterized in that the period of referring to ultrasonic transducers, i.e., starting said transducers) is assumed as a function of the inspection pig travel speed inside the pipeline and set by rotating the probe head.
However, said method suffers from the disadvantage that instantaneous slip of the probe head (or odometer wheel) which is typical in inspection of oil-pipelines, results in skipping some pipeline portions due to zero probing signals when the probe head (or odometer wheel) is at standstill. Additionally, the method discussed above cannot be used for inspecting long-distance pipelines due to the fact that the probing device used for carrying out the method, lacks self-containing feature.
The prototype to the proposed method is a method for in-tube flaw detection (EP0684446xe2x80x94Nov. 29, 1995 (relevant patent documents: U.S. Pat. No. 5,460,046, JP7318336) by passing inside the pipeline the inspection pig which carries reference transducers responsive to the pipeline diagnostic parameters, means for measuring, processing, and storing the measured data, by making periodical reference to said reference transducers, processing and storing the data measured by said transducers.
The cardinal disadvantage inherent in said method resides in that an excessive scanning occurs on the travel portions where the inspection pig travel speed is decreased (with the preset rate of referring to the transducers), said excessive scanning resulting in an increased amount of measured data per unit length of pipeline and, accordingly, in unreasonable use of the data storage element.
The herein-proposed method for in-tube flaw detection is carried into effect by passing inside the pipeline the inspection pig which carries reference transducers responsive to the pipeline diagnostic parameters, means for measuring, processing, and storing the measured data, by making periodical reference to said reference transducers, processing and storing the data measured by said transducers.
The herein-proposed method differs from the prototype in that in the course of passing the inspection pig with a period not less than the period of referring to reference transducers, inspection pig travel speed is determined, and the period of referring to reference transducers is assumed as a function of at least two values of inspection pig travel speed found in the course of passing said inspection pig.
The main technical result attainable by realizing the proposed invention consists in that the fact of referring to reference transducers at a period of time depending on the speed of the inspection pig travel through the pipeline enables one to estimate the data storage capacity depending on the pipeline distance to be inspected, thereby avoiding overflow of data storage devices in the case of a decelerated motion of the inspection pig or its transitory jamming in the pipeline. Moreover, a change in the duration of the period of referring to ultrasonic transducers depending on at least two values of inspection pig travel speed determined in the course of passing said inspection pig allow of obviating an unjustified change in the duration of said period in the case of a short-time change in the inspection pig travel speed.
It is in the course of passing of the inspection pig at the abovementioned period of time (that is, the period of determining the inspection pig travel speed) that an average travel speed of the inspection pig is determined for a certain lapse of time not in excess of the period of determining the aforesaid average travel speed of the inspection pig.
Calculation of an average travel speed of the inspection pig for short lapses of time (on the order of 1 to 10 s) allows of avoiding an adverse effect of transient changes in the line speed on estimation of a required period of referring to the reference transducers.
The duration of the period of referring to the reference transducers is considered to be a function of an average inspection pig travel speed as determined for the aforesaid lapse of time and of at least one value of the average inspection pig travel speed as determined for a certain previous lapse of time.
Period of determining the aforestated inspection pig travel speed is assumed as a function of the aforementioned period of referring to reference transducers. Period of determining the aforestated inspection pig travel speed equals N the aforementioned periods of referring to reference transducers, the numerical value of N ranging from 200 to 2000.
Insofar as the period of referring to reference transducers is considered to be a function of a number of measured values of the inspection pig travel speed so as to keep stable resolving power throughout the pipeline distance, so fixing the instance of determining the inspection pig travel speed to the period of referring to reference transducers makes possible taking measurements of said travel speed as a function of time, thus providing uniform measurement of the pig travel speed along the pipeline distance. With the value of N exceeding 2000, with large periods of referring to reference transducers (respectively, with a low pig travel speed), and with an abrupt increase in the pig travel speed information about these facts will be less operative, with the result that no diagnostic information will be available from a respective the pipeline portion. On the other hand, with lower values of N and high pig travel speed the measured speed values will be distorted due to transient accelerations and vibrations.
The aforestated period of referring to reference transducers is given a value selected from several discrete values (at least three in number). To each of said discrete values of a period of referring to reference transducers corresponds the range of the aforestated inspection pig travel speed either average or instantaneous).
As a further development of the present invention, to each of the aforementioned discrete values of a period of referring to reference transducers corresponds a first range of the inspection pig travel speed, said range being used for changing (decreasing) the period of referring to reference transducers (repetition period of the probing pulses) (in the case of an increase in the pig travel speed for a certain lapse of time), and a second range of the inspection pig travel speed, said range being used for changing (increasing) the period of referring to reference transducers (repetition period of the probing pulses) (in the case of a decrease in the pig travel speed for a certain lapse of time).
Provision of two speed ranges for each value of the period of referring to reference transducers allows of realizing the hysteresis in the period/speed relationship. Thus, in cases where a certain threshold speed value is surpassed and the period of referring to reference transducers is reduced correspondingly, a reverse extension of said period occurs not until travel speed is reduced to a value less that the aforestated threshold value. This makes it possible to stabilize operation of all electronic devices and apparatus involved in measurements and conversion of measured data with an adequately uniform pig travel at a speed approximating the threshold value or slightly deviating therefrom.
The preferred embodiment of the proposed method is the one wherein the lower limit of a first speed range is in excess of the lower limit of a second speed range, the upper limit of a first speed range exceeds the upper limit of a second speed range, the lower limit of a first speed range is less than the upper limit of a second speed range, a difference between the lower limits of the first and second speed ranges and/or between the upper limits of the first and second speed ranges is not more than 0.5 m/s.
When the inspection pig travel speed decreases for a certain lapse of time within which the speed value goes beyond the limits of a respective speed range, the period of referring to reference transducers (repetition period of the probing pulses) is changed at a time delay of from 10 to 100 s.
The fulfillment of said condition allows one to assure an adequate resolving power in cases where the travel speed drops down but transiently (i.e., for a lapse of time below 10 s), whereas an increase in the period of referring to reference transducers for a lapse of time that follows immediately after the instance of measuring (determining) the travel speed (with a travel speed increasing just in said lapse of time would result in an undesirable increase in resolving power affecting adversely the latter.
As a further development of the present invention, in the course of passing the inspection pig ultrasonic probing pulses are emitted and reflected pulses are received, corresponding to said emitted pulses, the pulse repetition period of said probing pulses being in fact the aforementioned period of referring to reference transducers.
The aforementioned average travel speed for a certain lapse of time is determined by measuring the distance passed by the inspection pig inside the pipeline for said lapse of time, using one or more odometers.
In a preferred embodiment of the present invention said distance is measured using at least two odometers, by determining changes in reading of either of the odometers taken for the aforementioned lapse of time, whereupon the higher reading of the two one is adopted as the distance passed for said lapse of time. Next said higher odometer reading is recorded as an increment in the distance passed inside the pipeline, and said increment in the distance passed is used in the course of the aforementioned determining of an average travel speed for a certain lapse of time.
Use of the abovementioned algorithm for determining the inspection pig travel speed makes it possible to obviate negative effects resulting from slippage of either of the odometers and, accordingly, a baseless change in the period of referring to reference transducers (of passing the probing pulses).